The invention relates to a digital pulse compression filter for a radar or sonar transmitting and receiving unit arranged for the generation and transmission of frequency-modulated transmitter pulses, the reception of echo signals, and the conversion of these signals into sampled and digitised signals.
Various embodiments of digital pulse compression filters are known. U.S. Pat. No. 3,680,105 describes a pulse compression filter utilising a frequency correlation circuit, multiplying the complex conjugate of the discrete Fourier transform of signals representing a replica of the transmitter pulse by the discrete Fourier transform of the sampled and digitised echo signals to obtain the compressed pulse from the obtained product signal through an inverse discrete Fourier transformation. The orthogonal components of the echo signal required for the discrete Fourier transformation are obtainable by quadrature detection in a conventional way. The orthogonal components of the signals representing the replica of the transmitter pulse need be calculated once only. U.S. Pat. No. 4,379,295 describes a digital pulse compression filter, where the orthogonal components of the echo signals obtained by quadrature detection are sampled, digitised and supplied to an FFT unit; the signals supplied over the various frequency output channels are each subjected to a specific delay and combined to form a compressed pulse. These pulse compression filters are however very complicated, while the latter pulse compression filter does not admit of a proper adaptation to the form of the transmitter pulse. The present invention has for its object to obviate these disadvantages to a high degree.